FROM: Jeff Coburn and Shelly Johnson, RTI International 

TO: Brenda Shine, EPA/OAQPS/SPPD 

FOR: Docket ID No. EPA-HQ-OAR-2010-0682 

DATE: September 20, 2013 

SUBJECT: MACT Analysis for Delayed Coking Unit Decoking Operations 

1. Purpose 

This memorandum discusses the procedure used to determine the maximum achievable control 

technology (MACT) standards for delayed coking unit (DCU) decoking operations. 

2. Background Information on DCU Operations 

The DCU uses thermal cracking to upgrade heavy feedstocks and to produce petroleum coke. 

Unlike most other refinery operations that are continuous, the DCU operates in a semi-batch 

system. Most DCU consist of a large process heater, two or more coking drums, and a single 

product distillation column. The DCU feed is actually fed to the unit’s distillation column. 

Bottoms from the distillation column are heated to near cracking temperatures and the resulting 

heavy oil is fed to one of the coking drums. As the cracking reactions occur, coke is produced in 

the drum and begins to fill the drum with sponge-like solid coke material. During this process, 

the DCU is a closed system, with the produced gas streams piped to the unit’s distillation for 

product recovery. 

When the first coke drum becomes filled with coke, the feed is diverted to the second coke drum 

and processing continues via the second coke drum. The full coke drum, which is no longer 

receiving oil feed, is taken through a number of steps, collectively referred to as decoking 

operations, to remove the coke from the drum and prepare the drum for subsequent oil feed 

processing. The decoking steps include: purging, cooling/quenching, venting, draining, 

deheading, and coke-cutting. A description of these steps and the potential emissions from these 

activities are provided in the next several paragraphs. Once the coke is removed, the vessel is resealed (i.e., the drain valve is closed and the “head” is re-attached), pressure tested (typically 

using steam), purged to remove oxygen, then slowly heated to processing temperatures so it can 

go back on-line. When the second coke drum becomes filled with coke, feed is diverted back to 

the first coke drum and the second drum is then decoked. In this manner, the DCU allows for 

continuous processing of oil even though the individual coke drums operate in cyclical batch 

fashion. 

The first step in decoking operations is to purge the coke drum with steam. This serves to cool 

the coke bed and to flush oil or reaction products from the coke bed. The steam purge is initially 

sent to the product distillation column and then diverted to the unit’s blowdown system. The 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

2 

blowdown system serves to condense the steam and other liquids entrained in the steam. Nearly 

all DCU operate a ”closed blowdown” system, such that uncondensed gases from the blowdown 

system are either sent to the product distillation column, the facility’s light gas plant, recovered 

as fuel gas, or combusted in a flare. In an open blowdown system, these uncondensed gases 

would be vented directly to atmosphere. The DCU vent discharge to the blowdown system is 

specifically defined in Refinery MACT 1 (40 CFR part 63, subpart CC) as the “delayed coker 

vent.” 

The next step in the decoking process is cooling/quenching the coke drum and its contents via 

the addition of water, commonly referred to as quench water, at the bottom of the coke drum. 

The water added to the vessel quickly turns to steam due to the high temperature of the coke bed. 

The water/steam helps to further cool the coke bed and “quench” any residual coking reactions 

that may still occur within the hot coke bed. As with the steam purge, steam off-gas from the 

cooling/quenching cycle is recovered in the unit’s blowdown system and this vent discharge is 

specifically defined in Refinery MACT 1 as the “delayed coker vent.” After several hours, the 

coke drum is sufficiently cooled so that water remains in the drum and the water level can be 

raised to entirely cover the coke bed. Although water covers the coke bed, the upper portion of 

the coke bed may still be well above 212 degrees Fahrenheit (°F) and steam will continue to be 

generated. In fact, since the coke drum vessel pressure is greater than atmospheric pressure, the 

equilibrium boiling point of water in the vessel is greater than 212 °F. Therefore, the water at the 

top of the coke drum is typically well above 212 °F (superheated water). As the coke drum and 

its contents continue to cool from the evaporative cooling effect of the steam generation, the 

steam generation rate and the pressure within the vessel will decrease. 

Owners or operators of DCU may use different indicators or set points to determine when the 

system has cooled sufficiently to move to the venting step; however, one of the most common 

indicators monitored is the pressure of the coke drum vessel (or steam vent line just above the 

coke drum, where steam exits the coke drum en route to the closed blowdown system). When the 

vessel has cooled sufficiently (e.g., when the coke drum vessel pressure reaches the desired set 

point), valves are opened to allow the steam generated in the coke drum to vent directly to the 

atmosphere rather than the closed blowdown system. This vent is commonly referred to as the 

“coker steam vent.” This is typically the first direct atmospheric emission release during the 

decoking operations when an enclosed blowdown system is used. While this vent gas contains 

predominately steam, methane and ethane, a variety of hazardous air pollutants (HAP) are also 

emitted with this steam. These HAP include light aromatics (e.g., benzene, toluene, and xylene) 

and light polycyclic organic matter (predominately naphthalene and 2-methyl naphthalene). HAP 

emissions from the DCU have been found to be a function of the quantity of steam generated 

(Coburn, 2013). 

In general, the next step in the decoking process is draining the water from the coke drum by 

opening a large valve at the bottom of the coke drum. The drain water typically falls from the 

coke drum onto a slanted concrete pad that directs the water to the coke pit area (where water 

and coke are collected and separated). Some DCU owners or operators initiate draining at the 

same time they initiate venting; other owners or operators may allow the vessel to vent for 20 or 

more minutes prior to initiating draining. While draining immediately may reduce the amount of 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

3 

steam exiting the unit via the stack, it is not expected to alter the overall emissions from the unit. 

During the venting and draining process, the pressure of the system falls to atmospheric. Steam 

will be generated until the evaporative cooling effect of that steam generation cools the coker 

quench water to 212 °F. If draining is initiated immediately, some of the superheated water may 

drain from the DCU before being cooled. A portion of that drained water will then flash to steam 

during the draining process as that superheated water contacts the open atmosphere. Therefore, 

draining quickly is not expected to alter the total amount of steam generated from the unit nor 

alter the overall emissions from the unit. It will, however, alter the relative proportion of the 

emissions that are released via the vent versus the quench water drain area. 

The next step in the decoking process is “deheading” the coke drum. At the top of the coke drum 

is a large 3- to 5-foot diameter opening, which is sealed with a gasketed lid during normal 

operations. When the steam generation rate from the coke drum has sufficiently subsided, this 

gasketed lid is removed to allow access for a water drill that will be used to remove coke from 

the drum. The process of removing this lid is referred to as “deheading” the coke drum. Different 

DCU owners or operators may use different criteria for when to dehead the coke drum. If the 

coke drum is deheaded soon after venting is initiated, some steam and associated HAP emissions 

may be released from this opening. As with draining, it is anticipated that the total volume of 

steam generated will be a function of the temperature/pressure of the coke drum. Deheading the 

coke drum prior to the coke drum contents reaching 212 °F will generally mean that some of the 

steam will be released from the coke drum head opening. However, this will not alter the total 

amount of steam generated; it merely alters the location of the release (steam vent versus coke 

drum head opening). The HAP emissions from the deheading process are expected to be 

proportional to the amount of steam released in the same manner as the emissions from the steam 

vent. 

The final step of the decoking process is coke-cutting. A high-pressure water jet is used to drill 

or cut the coke out of the vessel. The drilling water and coke slurry exits the coke drum via the 

drain opening and collects in the coke pit. Generally, the coke drum and its contents are 

sufficiently cooled so that this process is not expected to yield significant HAP emissions. 

However, if the other decoking steps are performed too quickly, hot spots may exist within the 

coke bed and HAP emissions may occur as water contacts these hot spots and additional steam 

and emissions are released. 

Once the coke is cut out of the drum, the drum is closed and prepared to go back on-line. This 

process includes pressurizing with steam to ensure there are no leaks (i.e., that the head is 

properly attached and sealed and the drain valve is fully closed). The vessel is then purged to 

remove any oxygen and heated by diverting the produced gas from the processing coke drum 

through the empty drum prior to sending it to the unit’s distillation column. A coke drum cycle is 

typically 28 to 36 hours from start of feed to start of feed. Delays in the decoking operations may 

impact process feed rates. That is, if the decoking and drum preparation steps take too long, the 

feed rate to the other coke unit must be reduced to prevent overfilling one coke drum prior to 

being able to switch to the other coke drum. This issue is less critical for DCU that operate with 

three or four drums per distillation column, but a consistent increase in the decoking times across 

all drums may still limit the capacity of the DCU at some petroleum refineries. 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

4 

3. Background Information of Regulatory Standards for DCU Decoking Operations 

Refinery MACT 1 includes delayed coker vents as an example within the definition of 

“miscellaneous process vent” (40 CFR part 63, subpart CC). However, Refinery MACT 1 goes 

on to exclude from the definition of miscellaneous process vent “Coking unit vents associated 

with coke drum depressuring at or below a coke drum outlet pressure of 15 pounds per square 

inch gauge [psig], deheading, draining, or decoking (coke cutting) or pressure testing after 

decoking” (see 40 CFR 63.641). Refinery MACT 1 defines a “delayed coker vent as “a vent that 

is typically intermittent in nature, and usually occurs only during the initiation of the 

depressuring cycle of the decoking operation when vapor from the coke drums cannot be sent to 

the fractionator column for product recovery, but instead is routed to the atmosphere through a 

closed blowdown system or directly to the atmosphere in an open blowdown system. The 

emissions from the decoking phases of delayed coker operations, which include coke drum 

deheading, draining, or decoking (coke cutting), are not considered to be delayed coker vents” 

(see 40 CFR 63.641 of subpart CC). The steam vent from depressurization is never mentioned in 

the definition of “delayed coker vent,” which focuses exclusively on the vent from the blowdown 

system. The steam vent is the place where HAP emissions would be vented to the atmosphere 

once they cease to be routed through the blowdown system. Thus, the steam vent is not 

considered a delayed coker vent, and it is excluded from being considered a miscellaneous 

process vent if it depressures at 15 psig or below. In other words, there is no applicable standard 

for atmospheric releases of delayed coker HAP emissions through the steam vent. 

We reviewed the background information from the development of Refinery MACT 1. Given the 

statements in the background information document for the August 1995 final Refinery MACT 1 

rule (EPA, 1995), the 15 psig pressure limit for the direct venting of the DCU to the atmosphere 

was not established as a MACT floor control level, but rather was established to accommodate 

all DCU at whatever pressure they typically switched from venting to the blowdown system to 

venting directly to the atmosphere. In addition, the U.S. Environmental Protection Agency (EPA) 

conducted a detailed information collection request (ICR) of the petroleum refining industry in 

2011 (EPA, 2011). The Refinery MACT 1 background information, along with data from the 

2011 Refinery ICR, refinery enforcement settlements and other information indicates that all 

refineries depressurize the coke drum below 15 psig, which indicates that all direct atmospheric 

releases (which occur through the steam vent) from the DCU decoking operations are excluded 

from the regulation. This exclusion, along with the additional exclusions for deheading, draining, 

coke cutting, and pressure testing after decoking indicates that there is not an applicable MACT 

standard for HAP emissions from the DCU. 

4. Evaluation of MACT Emission Limitations for DCU Decoking Operations 

Based on our review of the existing requirements in Refinery MACT 1, it is evident that HAP 

emissions occur during DCU decoking operations and that these emissions are not subject to 

MACT emission limitations. Therefore, we evaluated these emission sources in order to identify 

appropriate MACT emission limitations for the DCU decoking operations. 

We first evaluated traditional controls for organic HAP from process vents, such as the use of 

incinerators, flares, carbon adsorbers, or condensers. These control systems are generally 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

5 

ineffective or not applicable given the high moisture content of the DCU steam vent. In order to 

control these vapors, the vent would have to be processed in a blowdown system where the water 

can be condensed and recovered and then the drier gas stream can then be controlled. If the vent 

stream is diverted to the unit’s blowdown system, then this vent discharge clearly meets the 

definition of a delayed coker vent and the uncondensed gas stream would require control under 

Refinery MACT 1 as a miscellaneous process vent. Thus, the longer the DCU coke drum is 

vented to the closed blowdown system, the more the DCU depressuring emissions can be 

controlled. Thus, establishing a lower pressure set point at which a DCU owner or operator can 

switch from venting to an enclosed blowdown system to venting to the atmosphere was 

identified as the primary control technique for reducing emissions from delayed coking 

operations. 

As described in the impact estimates for DCU, organic HAP emissions from the decoking 

operations are a function of steam generation. Essentially, there is a fixed quantity of steam that 

will be generated as the coke drum and its contents cool to 212 °F (the boiling point of water at 

atmospheric pressure). As the coke bed cools, steam generation rates fall and the coke drum 

vessel pressure falls. Thus, the coke drum vessel pressure is an indicator of the average coke bed 

temperature. A lower coke drum vessel pressure set point will require the DCU to vent to the 

closed blowdown system longer, where the organic HAP can be recovered or controlled, and will 

allow the coke drum contents to cool further prior to atmospheric venting. This will result in less 

steam generation and fewer HAP emissions during the venting, draining and deheading process. 

Refinery NSPS Ja (40 CFR part 60, subpart Ja) establishes a pressure limit of 5 psig prior to 

allowing the coke drum to be vented to the atmosphere. Based on a review of permit limits and 

consent decrees, we found that coke drum vessel pressure limits have been established (and 

achieved) as low as 2 psig. There are 75 operating DCU according to the Refinery ICR responses 

(EPA 2011), so the sixth percentile is represented by the fifth-best performing DCU. 

We researched permits, consent decrees, Refinery ICR responses, and other rules addressing 

DCU depressurizing limits. Out of the 75 DCU, we identified at least 27 DCU that either 

currently operate or are required to operate by venting to the atmosphere only after the coke 

drum vessel pressure has reached 2 psig or less. Table 1 summarizes these results. Many of the 

refinery owners or operators claimed their DCU operation data as confidential business 

information (CBI). Therefore, we only specifically identify a facility due to permit or consent 

decree requirements. For these facilities, we only indicate whether their response to the ICR 

question regarding typical DCU vessel pressure when first venting to the atmosphere when they 

did not claim this information as CBI. For all other facilities, we blinded the facility 

identification. Eight DCU were identified that had a consent decree, permit, or local rule 

requiring these units to not depressure directly to the atmosphere until the DCU coke drum 

vessel pressure is 2 psig or less. While the Hovensa plant is not operating, the limit and consent 

decree will remain in place for the unit if operation begins again. The South Coast Air Quality 

Management District (SCAQMD) Rule 1114 that was adopted May 3, 2013 requires units to 

reduce the DCU vessel pressure to less than 2 psig prior to venting to the atmosphere. The 

SCAQMD rule is effective November 1, 2013, but includes provisions for owners or operators 

unable to comply with the 2 psig limit by November 1, 2013, to temporarily comply with a 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

6 

higher venting pressure limit for a certain time period prior to requiring all DCU to meet the 

2 psig venting pressure limit. Units 7 and 8 indicated in their Refinery ICR response that they 

typically vent at pressures below 2 psig. As such, these two units will be required by rule to vent 

at vessel pressures below 2 psig effective November 1, 2013. Therefore, we counted these units 

as having existing limits of 2 psig or less. DCU 9-11 indicated operating at the proposed 

conditions, but these units are only required by the Bay Area Air Quality Management District 

(BAAQMD) 8-10-301 standards to vent at a maximum pressure of 4.6 psig. The remaining units, 

12-27, indicated operating venting levels at or below 2 psig. However, we could not identify 

anystate or local requirements or permit conditions limiting the venting pressure for these units.
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

7 

Table 1. DCU Meeting the 2 psig Depressurizing Limit 

No. Company City State Unit 

Operating 

at or 

below 2 

psig limit 

in 2010a

Type 

of 

Limitb

Limit 

Date of 

Permit or 

Consent 

Decree 

Re

1 BP Whiting IN New 

Coker 

 CD Shall not commence Coke 

Drum Venting until the Coke Drum Overhead Pressure is 2.0 psig or less

9/28/12 

2 Marathon Detroit MI Coker P Shall not vent the active 

coke drum to the atmosphere until the end of the coking cycle, when the drum pressure is 2 psig or less 

1/11/12 

3-4 Marathon Garyville LA Unit 5 

Coker, Unit 205 Coker 

Yes P Shall relieve the Coker 

Drum Vents at a pressure equal to or less than 2 psig during atmospheric venting

8/29/13 

5 ConocoPhillips Co., 

WRB Refining, LP 

Wood River 

IL Coker 2 CD Coke Drum OH Pressure 

Limit of 2 psig for the Coker 2 Coke Drums 

2/28/12 

6 Hovensa St. Croix USVI Delayed 

Coker Unit 

 CD Shall comply with a 

depressurization level of 2 psig for the Coker Steam Vents 

1/26/11 

7-8 "7-8" "7-8" CA "7-8" Yes RA Shall depressurize each 

coke drum to less than two (2) pounds per square inch, gauge (psig) prior to venting it to atmosphere 

 Sou

Air MaDis
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

8 

No. Company City State Unit 

Operating 

at or 

below 2 

psig limit 

in 2010a

Type 

of 

Limitb

Limit 

Date of 

Permit or 

Consent 

Decree 

Re

9-11 "9-11" "9-11" CA "9-11" Yes RA Shall be vented through a 

knock-out pot and then abated in one of the following ways, to as low a vessel pressure as possible, but at least until pressure is reduced to less than 1000 mm Hg (4.6 psig)c

 Bay 

QuMaDis

12-27 

"12-27" "12-27" varies "12-27" Yes None 

a As reported in response to the Refinery ICR. This information was often claimed as CBI. b “Type of Limit” indicates what regulates the limit: CD = consent decree; “P” = Permit; “RA” = Regulatory Agency. c mmHg = millimeters of mercury. 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

9 

While we identified eight DCU with permit requirements or consent decrees specifying a coke 

drum venting pressure limit of 2 psig, we did not identify any permit or consent decree 

requirements more stringent than 2 psig. Refinery owners and operators were asked to provide 

the “typical coke drum pressure just prior to venting” for each DCU in their responses to the 

Refinery ICR, and the responses indicate that four DCU operate such that the typical venting 

pressure is 1 psig or less. However, this “typical coke drum pressure” does not represent a not-tobe-exceeded pressure limit, but rather is indicative of a vessel that is operated to meet a not-tobe-exceeded pressure limit of 2 psig. We do not have information to indicate whether these 

facilities can always depressurize at 1 psig or less, whereas in order to be in compliance with 

their permit limits, the best-performing sources must be able to depressurize at 2 psig or less at 

all times. Therefore, the MACT floor for DCU decoking operations is to depressure at 2 psig or 

less prior to venting to the atmosphere for both new and existing sources. 

We then considered control options beyond the floor level of 2 psig to determine if additional 

emission reductions could be cost-effectively achieved. We considered a control option that 

allowed atmospheric venting only after the DCU vessel pressure reached 1 psig or less, since 

some facilities reported in the ICR depressurizing to that level prior to venting. There are several 

technical difficulties associated with establishing a pressure limit at this lower level. First, the 

lowest pressure at any point in a closed blowdown system is generally designed to be no lower 

than 0.5 psig in order to prevent air ingress into the unit in the event a valve, flange, or other 

component leaks. Air ingress into the DCU or blowdown system has the potential to create an 

explosive atmosphere. Consequently, for safety reasons, the DCU compressor system would 

operate with an inlet pressure of no less than 0.5 psig. Second, there are several valves and 

significant piping (for cooling and condensing steam) between the DCU drum and the recovery 

compressor. There is an inherent pressure drop when a fluid flows through a pipe or valve. Two 

valves are used for all DCU lines to make sure that the unit is either blocked off from the 

processing fluids or blocked in so there are no product losses out the steam line during 

processing. Considering the need for two valves and piping needed in the cooling system, DCU 

designed for a minimal pressure loss will generally still have a 0.5 to 1 psig pressure drop 

between the DCU drum and the recovery compressor inlet. Finally, in order to meet a 1 psig 

pressure limit at all times, the DCU closed vent system would need to be designed to achieve a 

vessel pressure of approximately 0.5 psig. Given the above considerations, we do not consider it 

technically feasible to routinely achieve a vessel pressure of 0.5 psig in order to comply with a 

never-to-be-exceeded drum vessel pressure of 1 psig. As noted previously, facilities that 

“typically” achieve vessel pressures of about 1 or less are expected to do so in order to meet a 

never-to-be-exceeded drum vessel pressure limit of 2 psig and no DCU is currently required to 

meet a drum vessel pressure limit of less than 2 psig for all venting events. 

We also evaluated additional work practice standards regarding draining, deheading, and coke 

cutting. As stated previously, the decoking emissions can be released from a variety of locations, 

and the 2 psig or less limit for depressurizing the coke drum will effectively reduce the emissions 

from all of these emission points. Although atypical, the owner or operator of a DCU may start 

draining water prior to opening the steam vent. Owners or operators may adopt this practice as a 

means to reduce pressure in the coke drum prior to venting the drum to atmosphere in order to 

achieve the venting pressure limit. Initiating water draining prior to reaching 2 psig would result 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

10 

in draining water that is hotter than it would be had the drum been sufficiently cooled (i.e., the 

pressure limit achieved) prior to draining the vessel, effectively diverting HAP emissions to the 

water drain area rather than capturing these HAP in the enclosed blowdown system, where they 

can be either recovered or controlled. Therefore, we recommend that the 2 psig limit apply to all 

potential release points in the decoking operations, including draining. 

We also considered whether there were means to connect the bottom of the coke drum to a large 

diameter “hose” so that the drained water and/or the coke cutting slurry could be discharged 

from the DCU and enter the coke pit in a submerged fill manner. This enclosed transfer, 

submerged fill requirement would reduce the emissions released during these processes. 

However, we could identify no commercially available equipment to connect the coke drum to 

the coke pit. There may also be technical issues associated with plugging of the drain hose 

during the coke cutting process. While submerged filling has been used to reduce emissions 

during a variety of transfer operations, we conclude that this is not a viable option for DCU at 

this time. 

We could not identify any other emission reduction options that could lower the emissions from 

the DCU decoking operations. Since we could not identify a technically feasible control option 

beyond the MACT floor, we recommend that the MACT floor pressure limit of 2 psig is MACT 

for both new and existing sources. 

5. Justification for Work Practice Standards for DCU Decoking Operations 

We believe that work practice standards are appropriate for the emissions associated with the 

DCU decoking operations. While the emissions from the DCU steam vent are released via a 

conveyance designed and constructed to emit or capture such pollutant, we believe that CAA 

section 112(h)(2)(B) applies in that it is not feasible to prescribe or enforce an emission standard 

for the DCU steam vent because the application of measurement methodology for this source is 

not practicable due to technological and economic limitations. The DCU steam vent typically 

contains 99-percent water, which interferes with common sample collection and analysis 

techniques. Also, the flow rate from this vent is not constant; rather, it decreases during the 

venting process as the pressure in the DCU coke drum approaches atmospheric pressure. Finally, 

the venting time can be very short, particularly for units complying with the proposed standards. 

Together, these factors make it extremely difficult to measure the emissions from the DCU steam 

vent. As part of the ICR, the EPA requested stack testing of eight DCU. After discussions with 

stack testing experts within the agency and with outside contractors used by industry to perform 

the tests, the EPA concluded that sources with venting times less than 20 minutes would not be 

able to perform an emissions test that would yield valid results. Therefore, only two of the eight 

facilities actually performed the tests. We anticipate all units complying with the proposed 

standards for DCU steam vents would vent for less than 20 minutes. 

Second, due to the interplay of the emission points associated with the decoking operations, it is 

possible to alter the amount of emissions released via the steam vent (conveyance) depending 

when the subsequent decoking steps are conducted. If draining and deheading are initiated 

quickly after venting, this will reduce the emissions discharged from the vent (although as 

explained above, it does not reduce the emissions from the collective set of decoking operations 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

11 

release points). Therefore, if the EPA regulates only the steam vent, owners or operators of DCU 

could divert the emissions from the steam vent to the drain or other release points. Thus, it is not 

feasible or effective for the EPA to enforce an emission standard only on the steam vent (i.e., 

only releases from the conveyed emissions) because the timing of draining and deheading can 

alter the portion of the decoking emissions that are released from the actual steam vent. 

Third, the emissions from the draining, deheading and coke cutting steps cannot be emitted 

through a conveyance designed and constructed to emit or capture such pollutant. For example, 

the coke drum head must be removed to provide an accessible opening in the drum so the coke 

cutting equipment can be lowered into the drum. This opening cannot be sealed during cokecutting because the drilling shaft will occupy the opening and the shaft must be free to be 

lowered or raised during the coke-cutting process. We believe that the 2 psig work practice 

standard prior to venting, draining or any other decoking step will effectively limit the emissions 

from all phases of the decoking process, including these release points that cannot be emitted 

through a conveyance and thereby meet the criteria for a work practice standard under CAA 

section 112(h)(2)(A). 

Consequently, due to the unique nature of the DCU decoking operation emissions, the 

difficulties associated with monitoring the DCU steam vent, and the inability to construct a 

conveyance to capture emissions from all decoking operation release points, we believe it is 

appropriate for the EPA to develop work practice standards to limit the emissions associated with 

DCU decoking operations. 

6. Evaluation of Cost and Environmental Impacts of MACT Emission Limitations for 

Delayed Coking Units 

DCU that cannot currently meet the 2 psig pressure limit would be expected to install a device 

(compressor or steam ejector system) to lower the DCU vessel pressure. In the Refinery NSPS Ja 

impact analysis, facilities not able to meet the pressure threshold were assumed to purchase and 

install a larger compressor to lower the blowdown system pressure (Coburn and Richardson, 

2008). Other approaches to lowering blowdown system (and coke drum) pressure exist. 

Specifically, steam ejectors have been identified as a method to help existing units depressurize 

more fully in order to achieve a set vessel pressure or drum bed temperature. Upgrading the 

closed vent system to reduce pressure losses or to increase steam condensing capacity may also 

allow the DCU to depressure more quickly while the emissions are still vented to the closed 

blowdown system. 

For existing sources, we assumed all DCU that reported a “typical drum pressure prior to 

venting” of more than 2 psig would install and operate a steam ejector system to reduce the coke 

drum pressure to 2 psig prior to venting to atmosphere or draining. The operating costs of the 

steam ejector system are offset, to some extent, by the additional recovered vapors. Vapors from 

the additional gases routed to the blowdown system contain high levels of methane 

(approximately 70 percent by volume on a dry basis) based on DCU steam vent test data. If these 

vapors are directed to the closed blowdown system rather than to the atmosphere, generally the 

dry gas can be recovered in the refinery fuel gas system or light-ends gas plant. This recovered 

methane is expected to off-set natural gas purchases for the fuel gas system. 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

12 

We anticipate that new DCU sources can be built with a closed blowdown system designed to 

achieve a 2 psig vessel pressure with no significant increase in capital or operating costs of the 

new DCU. There may be a slight increase in capital costs for the low pressure valve design or for 

larger diameter piping; however, these design improvements generally lower the operating costs 

of the DCU. For example, designing the system to vent at a lower pressure results in additional 

vapor recovery, which is expected to off-set any additional capital costs associated with the low 

pressure design closed blowdown system. 

The costs of complying with the 2 psig coke drum threshold prior to venting or draining are 

summarized in Table 2. The costs are approximately $1,000 per ton of volatile organic 

compounds (VOC) reduced and approximately $5,000 per ton of organic HAP reduced when 

considering VOC and methane recovery credits. Additional detail regarding the cost and 

environmental impact estimates are provided elsewhere (Coburn, 2013). 

Table 2. Nationwide Emissions Reduction and Cost Impacts of Control Option for 

Existing Delayed Coking Units at Petroleum Refineries 

Control 

Option 

Capital 

Cost 

(million $) 

Annualized 

Costs 

Without 

Recovery 

Credits 

(million 

$/yr) 

Emissions 

Reduction, 

VOC (tpy)a

Emissions 

Reduction, 

HAP (tpy)a

Cost Effectiveness 

($/ton 

HAP) 

Total 

Annualized 

Costs with 

VOC 

Recovery 

Credit 

(million 

$/yr) 

Overall Cost 

Effectiveness with 

VOC 

Recovery 

Credit ($/ton 

HAP) 

2 psig 52 10.2 4,250 850 12,000 3.98 4,700 

a

 tpy = tons per year. 

7. References 

BAAQMD (Bay Area Air Quality Management District). 2004. Process Vessel Depressurizing, 

Regulation 8, Rule 10-301. Last Amended 1/21/04. 

http://hank.baaqmd.gov/dst/regulations/rg0810.pdf. [Accessed 9/16/2013]. 

Coburn, J. 2013. Impact Estimates for Delayed Coking Units. Memorandum to Brenda Shine, 

U.S. EPA, from Jeff Coburn, RTI International. Revised September 12, 2013. 

Coburn, J. and C. Richardson. 2008. Final Impacts Analysis for Delayed Coker Depressurization 

Emissions. Memorandum from Jeff Coburn and Carrie Richardson, RTI International, to Bob 

Lucas, EPA/SPPD. April 28, 2008. Docket Item No. EPA-HQ-OAR-2007-0011-0226. 

Consent Decree. 2011. United States of America and The United States Virgin Islands, Plaintiffs, 

v. HOVENSA LLC, Defendant. 1:11-cv-00006. Filed 1/26/2011. 

http://www2.epa.gov/enforcement/hovensa-llc-clean-air-act-settlement. [Accessed 

9/11/2013]. 
Technical Memorandum – MACT Analysis for Delayed Coking Unit Decoking Operations 

September 20, 2013 

13 

Consent Decree. 2012a. The United States of America, State of Illinois, State of Louisiana, State 

of New Jersey, Commonwealth of Pennsylvania, Northwest Clean Air Agency, Plaintiffs v. 

ConocoPhillips Company, WRB Refining LP, Defendants. 4:05-cv-00258. Filed 2/28/2012. 

http://www2.epa.gov/enforcement/third-amended-consent-decree-conocophillips-companywrb-refining-lp-civil-action-no-h-05. [Accessed 9/11/2013]. 

Consent Decree. 2012b. United States of America and The State of Indiana, Plaintiffs, and The 

Sierra Club, Save the Dunes, The Natural Resources Defense Council, The Hoosier 

Environmental Council, Susan Eleuterio and Tom Tsourlis, Plaintiff-Intervenors, v. BP 

Products North America Inc. Defendant. 2:12-cv-00207. Filed 5/23/2012. 

http://www2.epa.gov/enforcement/bp-whiting-settlement-flaring. [Accessed 9/11/2013]. 

EPA (U.S. Environmental Protection Agency). 1995. National Emission Standards for 

Hazardous Air Pollutants Petroleum Refineries - Background Information for Final 

Standards; EPA-453/R-95-015b. Office of Air Quality Planning and Standards, Research 

Triangle Park, NC. July. 

EPA (U.S. Environmental Protection Agency). 2011. Petroleum Refinery Database, based on 

Refinery Information Collection Request (ICR) for Calendar Year 2010. September 2011. 

Docket Item Nos. EPA-HQ-OAR-2010-0682-0061 through 0069. 

LDEQ (State of Louisiana Department of Environmental Quality: Environmental Services). 

2013. Marathon Petroleum Co LP-LA Refining Division- Garyville Refinery, Title V 

Regular Permit Minor Mod: 2580-00013-V11. 8/29/2013. 

MDEQ (Michigan Department of Environmental Quality: Air Quality Division). 2012. Marathon 

Petroleum Company LP, Permit to Install: 63-08C. 1/11/2012. 

SCAQMD (South Coast Air Quality Management District). 2013. Petroleum Refinery Coking 

Operations, Rule 1114. Adopted May 3, 2013. 

http://www.arb.ca.gov/DRDB/SC/CURHTML/R1114.PDF. [Accessed 9/11/2013].